Electric switching devices

ABSTRACT

An electric relay operative to effect switching operations at predetermined amplitude levels of a controlling current whose amplitude fluctuates relatively slowly with respect to time, such as the output of a light sensitive device subjected to daylight. The relay comprises a pair of switch contacts whose movements towards and away from each other are controlled by a latching lever system, the operating motions for said latching lever system being provided by a bimetal element which is subjected to heat from an electric heater arranged for energisation by the fluctuating control current.

O United States Patent 1191 3,827,009 Thomas July 30, 1974 1 ELECTRIC SWITCHING DEVICES 3,546,651 12/1970 Moorhead et al. 337/101 x 9 C l 337 I 1 1 Inventor: David Ellis Thomas, Enfieldi $125328 11133; T3353? 337110? England 3,702,454 11/1972 Brown 337/77 [73] Assignee: Sangamo Weston Limited, Enfield,

Middlesex, Engla d Primary ExaminerA. T. Grlmley i F Y & Th Filed: J 1973 Attorney Agent or irm oung ompson [2l] Appl. No.: 323,428 [57] ABSTRACT An electric relay operative to effect switching opera- Foreign Application Priority Data tions at predetermined amplitude levels of a controliaii. 25. 1972 Great Britain 3496/72 ling Current Whose amplitude fluctuates relatively slowly with respect to time, such as the output of a [52 us. c1 337/77, 337/51, 337/99 light Sensitive device Subjected to daylight. The relay 5 "01 1 02 comprises a pair of switch contacts whose movements 58 Field or Search 337/46, 49, 51, 70, 77, wards and away from each other are controlled y a 337 7 99 1 0; 10 200 R latching lever system, the operating motions for said latching lever system being provided by a bimetal ele- 5 References Cited ment which is subjected to heat from an electric UNITED STATES PATENTS heater arranged for energisation by the fluctuating control current. 2.7 8.223 5/1956 Frank 337/100 2. 2.548 2/1959 Christensen 337/101 X 13 Claims, 10 Drawing Figures H 4 77 I r 1 l c 196 Z b a l .J 3 A 14 x 9 ELECTRIC SWITCHING DEVICES This invention relates to electric switching devices and is more particularly concerned with switching devices adapted for operation at chosen amplitude levels of an operating current whose amplitude fluctuates relatively slowly with respect to time, such as the current output from light sensing means subjected to daylight. The invention is particularly suitable for use in controlling street lighting and other apparatus in dependence upon the value of ambient light.

The more usual form of switching devices for operation by light sensing means sensitive to daylight and currently employed for the control of street lighting is one in which, after effecting switch on at the time when the ambient daylight has descreased to a chosen level at the onset of darkness during the evening, the light level at which the subsequent switch of operation takes place during the time of increasing ambient daylight level on the following morning, is a somewhat higher light level than such chosen level. This delay or time differential is clearly wasteful; such wastage is often aggravated by the fact that some types of lamps, such as sodium and mercury vapour lamps commonly employed for street lighting purposes, need to be switched on earlier, i.e., at a higher chosen level at the evening period in order to allow for the warming up period necessary before the full illumination level of the lamp is provided.

One object of the present invention is to provide an improved switching device in which the above switching time differential can be materially reduced or even eliminated altogether. Another object of the invention is to provide an improved switching device in which a switceing time differential of opposite sense to that described above is provided in order to allow for the initial warming up period of certain types of lamp, such as sodium and mercury vapour lamps. A further object of the invention is to provide an arrangement in which the necessary switch operating power is reduced to a low level in order to permit the employment of cheaper and light-sensitive devices in the associated control system.

In accordance with this invention an electric switching device comprises first and second relatively movable contact members carrying respective first and second switch contacts, a bimetal element operative to provide switch controlling motion in a first direction during heat thereof and in a second opposite direction during cooling thereof and coupling means including first and second latch means between said bimetal element and said first and second contact members, said first latch means being tripped during movement of said bimetal element in said first direction to allow relative movement between said contact members to place said switch contacts in a first switching condition and said second latch means being tripped during movement of said bimetal element in said second direction to allow relative movement between said contact members to place said switch contacts in a second switching condition. y

In a particular form of the invention a bimetal system is arranged to control the movement of said switch contacts which can form-part of the controlled load circuit through the intermediary of a latching lever system comprising two latch levers arranged to permit the respective closing and opening operations of said switch contacts to occur at different levels of energization of said electric heater, thereby to permit the switch on" and switch off operations to occur at different levels of ambient light. The above-mentioned time differential may in this way be reduced, eliminated or even reversed in sense.

In order that the nature of the invention may be more readily understood one particular construction embodiment will now be descirbed by way of illustrative example only and with reference to the accompanying drawings in which:

FIG. 1 is a front elevational view of a switching device constructed in accordance with the invention.

FIG. 2 is a side elevation of the device of FIG. 1 taken in the direction of the arrow II, FIG. 1.

FIG. 3 is an underside view of the same switching device taken in the direction of the arrow III, FIG. 1.

FIG. 4 is a fragmentary side elevation showing the particular form of construction of one end of one of two switch contact blades.

FIG. 5 is a fragmentary front elevational view of one of the latching levers showing its relationship to the cooperating portions of the two switch contact blades.

FIG. 6 is a fragmentary elevational view, similar to FIG. 5, showing the other of the latching levers with relationship to the associated switch contact blades, while FIGS. 7a, 7b, 7c, and 7d comprise a series of four simplified and largely disgrammatic elevational views showing the device of FIGS. 1-6 in four different operative positions which it assumes during a complete switching cycle from off through on to of again.

Referring now more particularly to FIGS. 1-6, the illustrated switching device comprises a baseboard 13 of insulating material upon which is secured a carrier plate 7 having an outwardly projecting lug 14 to which is rigidly secured one end of a bimetal blade 8 of a bimetal system. This bimetal blade 8 is an ambient temperature compensating member and its opposite end is rigidly attached, through the intermediary of an insulating block 15, to one end of a bimetal operatingblade 9 forming a second component of said bimetal system. This blade 9 extends downwardly and in substantially parallel relationship to the compensating blade 8 and at its opposite, lowermost, end engages and controls the movement of two latch levers 3, 4 of a latching lever system. The two levers are arranged side by side and are each independently pivotally mounted upon a common horizontal pivot pin 5 which is also rigidly secured to the baseboard 13.

An electric heater l0, conveniently a ceramic substrate type of heater, is positioned to abut against one side of the bimetal operating blade 9 and is held against such blade by means of leaf springs 11 and 12 with a light pressure insufficient materially to affect the operating forces provided by the bimetal system. The two leaf springs 11 and 12 are each attached by one end to opposite ends of the heater l0 and themselves have their opposite ends rigidly secured respectively to separate fixed anchorage points on the baseboard 13. The anchorage point for the blade 12 is a metal stud l6 rigidly secured in the baseboard 13 while the corresponding anchorage point for the blade 11 is one of the securing rivets associated with a mounting lug 18a which is also rigidly secured to the baseboard 13. In addition to supporting the heater 10, the leaf springs 11 and 12 serve for providing the necessary electrical connection thereto, suitable wiring extending from the two anchorage points to the associated light-sensing means 17. The spring arrangement is such that the substrate heater closely follows the movement of the bimetal operating blade 9 to provide efficient heat transfer thereto at all times. Heating of the blade 9 via the heater 10 by current output from the associated light sensing means 17 causes movement of the lower end of such blade 9 in the direction of the arrow x. Conversely, cooling of the blade results in movement of the blade end in the opposite direction of arrow y.

Adjacent to and parallel with the mounting lug 18a is a second mounting lug 18b also rigidly secured to the baseboard 13. To the mounting lug 18a is rigidly secured the upper part of a spring contact blade 2, while to the other lug 18b is similarly secured the upper part of a second spring contact blade 1. The two blades 1 and 2 carry facing contacts 20a, 20b, respectively. The contact blades 1 and 2 are arranged to be biased by their inherent springy nature in the respective directions of the arrows a and b, the biasing being such that, if not otherwise controlled, the two contacts 20a, 20b close circuit. The contacts 20a, 20b serve for effecting control of the external power or load circuit, such as an associated street lighting lamp, through connections taken from the upper ends of the contact blades 1 and 2.

Referring now to the latching lever system in greater detail, it will be seen that the inner latch lever 3 lying nearest to the baseboard 13 has a substantially horizontally directed limb 3a which extends through an aperture 2a in the contact blade 2 and into an aperture 1b in the contact blade 1. The same latch lever also has an upwardly directed arm 3b terminating in a nose portion 30 which can bear against that side of the operating bimetal blade 9 which is facing the compensating blade 8. This latch lever 3 is biased by means of a helical spring 6 surrounding the pivot pin 5 and coupled respectively at its opposite ends with a tail 3d of the latch lever 3 and an aperture 13a in the baseboard 13 so as normally to bias the latch lever to rotate in a clockwise direction (FIGS. 1 and 6) and thereby to maintain the nose 3c in contact with the operating bimetal blade 9. The underside of the lever arm 3a is provided with a step 3e for a purpose which will be described later.

The outermost latch lever 4 also has a horizontally directed limb 4a which also extends through opening 2a in the contact blade 2 and then towards or even through a second aperture 1a in the contact blade 1. This latch lever 4 has an upwardly extending portion which is shaped to form a neck region 4b which embraces the thickness of the lower end of the operating bimetal blade 9 and also with a further nose region 4c which bears against the surface of the inner switch blade 2, facing the operating bimetal blade 9. As shown more clearly in FIG. 4, the inner switch blade 2 has a single complex shaped aperture 2a, whereas referring to FIG. 2, the outer blade 1 has two separate apertures 1a and lb which are aligned respectively with different portions of the said complex aperture 2a in blade 2.

Referring mow more particularly to the various diagrams of FIGS. 7a-7c, FIG. 7a shows the relative positions of the various parts under the condition, such as during daylight, when the power input from the source energizing the heater 10 is at a maximum. Under such condition of high current input to the heater 10, the bimetal operating blade 9 deflects so that its lowermost 'end moves to the left thereby moving the nose 4c of latch lever 4 anticlockwise to allow the associated contact blade 2 also to move leftwards; the contact 20b is separated from the facing contact 20a due to the engagement, in a manner which will be made clear later, of the tip of the arm 4a of the same latch lever 4 against the left-hand face of the contact blade 1, thereby preventing the inherent spring bias of that blade from op erating to cause the contact 20a to follow contact 20b. The switch contacts are accordingly held open and the controlled lamp or other device is de-energized.

During subsequent decrease of the heat input to the heater 10 on account of lowered illumination of the associated light sensing means, such as during the onset of evening, the lower end of the bimetal blade 9 moves towards the right as shown in FIG. 7b to cause the coupled latch lever 4 to rotate clockwise about the pivot pin 5. In addition to moving the switch blade 2 to the right by the clockwise movement of the nose 4c of the latch lever 4, the accompanying lowering of the arm 40 causes the tip of such arm to move into the slot la (see FIG. 2) in the switch blade 1 thereby removing the previous retention of that blade against its inherent spring bias and allowing the two contacts 20a and 20b to close and so complete the energization circuit of the associated lamp or other device.

During the following, darkness, period of still further reduced heat input to the heater 10 from the associated light sensing means, continued movement of the lower end of bimetal blade 9 in direction y causes further rocking movement of the latch lever 4 in a clockwise direction and accompanying further movement to the right of the associated nose 40. As may be seen from FIG. 70, this movement, in addition to moving the contact blade 2 towards the right, also causes similar movement to the right of the opposing contact blade 1 through the mechanical transmission link provided by the engaging closed contacts 20a, 20b. A position is reached at which the other latch lever 3, on account of its applied spring-biasing for movement in a clockwise direction, has the end of its arm 3a fall out of the slot 1b (see FIG. 2) in the contact blade 1 and the position eventually reached is one in which, on account of still further movement to the right of both of such control blades 1, 2, the step 3e on the latch lever 3 drops behind the adjacent edge of the aperture (see FIG. 4) of the other contact blade 2. During this movement of the two switch blades there is some degree of relevant sliding motion between the closed contacta 20a, 20b, and this serves to shear any small welds which may have occurred during the preceding contact closing operation and so operates to maintain the contacts in good operative condition.

During the next following period of increasing current input to the heater 10 from the associated light sensing means, as at the onset of morning, the latch levers 3 and 4 begin to be moved, in an anticlockwise direction, by the now leftward movement, arrow x, of the lower end of the operating bimetal blade 9 as shown in FIG. 7d. This movement eventually results in the release of the contact blade 2 by the lifting of the step 3e on the latch lever 3 from the edge of the slot 2a in such blade while the contact blade 1 is still maintained towards the right by the abutment of the end face of the arm 3a of the latch lever 3 against the left-hand surface of such contact blade I. This causes the controlled circuit contacts a, 20b to be opened suddenly at the instant when the step 3e slips from the edge of the opening 2a. Upon still further increase of heat current input from the associated light sensing means the system eventually returns to the initial starting condition as shown in FIG. 7a by the release of the contact blade 1 due to entry of the tip of the arm 3a of the latch lever 3 into the slot 1b in that contact blade. Closure of the switch contacts 20a, 20b is prevented by engagement of the end of arm 4a of lever 4 with the blades.

The latch lever system permits rapid movement of the switch blades and power contacts and ensures that the duration of zero contact pressure between such contacts is at a minimum while permitting the use of relatively light operating forces relative to the contact pressures actually provided between the power contacts.

If the requirements are such that there is to be no dif ferential between the switch on and switch off current input levels, the position of the operating bimetal blade 9 at which the tip of the arm 4a of the latch lever 4 slips off the edge of the slot 1a in contact blade 1 (FIG. 7b) is arranged to be the same as that at which the step 3e on latch lever 3 releases the edge of slot 2a in' contact blade 2 (FIG. 7d). To provide a differential in a direction such as to suit sodium and mercury vapour lamps, the position of the operating bimetal blade 9 necessary to effect switch on, as in FIG. 7b, is made to correspond to a heat input higher than the heat input necessary to arrive at the switch of condition shown in FIG. 7d.

What we claim is:

1. An electric switching device comprising first and second relatively movable-contact members carrying respective first and second switch contacts, a bimetal element operative to provide switch controlling motion in a first direction during heating thereof and in a second opposite direction during cooling thereof and coupling means including first and second latch means between said bimetal element and said first and second contact members, said first latch means being tripped during movement of said bimetal element in said first direction to allow relative movement between said contact members to place said switch contacts in a first switching condition and said second latch means being tripped during movement of said bimetal element in said second direction to allow relative movement between said contact members to place said switch contacts in a second switching condition.

2. An electric switching device as set forth in claim 1, and an electric heater located adjacent said bimetal element and terminal means for connecting said heater to a source of control current whereby the temperature of said bimetal element varies with the amplitude of the applied control current.

3. An electric switching device according to claim 2 form and said electric heater is of similar strip-like shape.

6. An electric switching device in accordance with claim 5 in which said electric heater is of ceramic substrate type.

7. An electric -switching device according to claim 5 in which said electric heater is supported by means of light flexible blade springs to abut said bimetal element without imparting any substantial displacement force thereto.

8. An electric switching device in accordance with claim 3 in which said bimetal system comprises two blade-form bimetal elements in spaced parallel relationship and rigidly interconnected with one another at one end, the opposite end of one blade element being fixed in position and forming an ambient temperature compensating member and the opposite end of the other blade element being coupled to said latching lever system.

9. An electric switching device according to claim 2 in which said latching lever system comprises two latch levers arranged to permit the respective closing and opening operations of said switch contacts to occur at different levels of energization of said electric heater.

10. An electric switching device according to claim 9 in which the closing operation of said switch contacts is arranged to occur at a level of energization of said electric heater which is higher than the subsequently occurring level of heater energization at which opening of said switch contacts occurs.

11. An electric switching device according to claim 9 in which said two latch levers are disposed in side-bysidev relationship and independently pivoted upon a common pivot pin, one of said latch levers being coupled to said bimetal element in a manner providing positive transmission of movement from such bimetal element in each of two opposing directions and the other of said latch levers being spring biased into coupling engagement with said bimetal to provide positive transmission of movement in one direction only.

12. An electric switching device in accordance with claim 2, and light sensing means connected to supply energizing current to said heater and at least one electric lamp connected for energization from a current supply source through said first and second contacts.

13. An electric switching device comprising stationary frame means, first and second resilient spring blades each secured at one end to said frame means and disposed in parallel facing relationship and each carrying one of a pair of cooperating electric contacts, a strip-form first bimetal element, a second ambienttemperature compensating bimetal element secured at one end to said frame means and at its other end to one end of said first bimetal element, an electric heater having terminal means for connection to a source of switch control current, resilient support means operative to maintain said heater in close heat transfer relationship to said first bimetal element during displacement of such first bimetal element during heating and cooling thereof and first and second latch levers each pivotally mounted on a common pivot secured to said frame means, each of saidlatch levers being coupled to the other end of said first bimetal element for rocking movement in accordance with the heating and cooling of said first bimetal element, said first latch lever having a nose operative during displacement of said first lever having a latch-forming limb cooperating with said first spring blade to maintain said contacts engaged with one another until a latch tripping point is reached during displacement of said first bimetal element in a direction opposite to said one direction. 

1. An electric switching device comprising first and second relatively movable contact members carrying respective first and second switch contacts, a bimetal element operative to provide switch controlling motion in a first direction during heating thereof and in a second opposite direction during cooling thereof and coupling means including first and second latch means between said bimetal element and said first and second contact members, said first latch means being tripped during movement of said bimetal element in said first direction to allow relative movement between said contact members to place said switch contacts in a first switching condition and said second latch means being tripped during movement of said bimetal element in said second direction to allow relative movement between said contact members to place said switch contacts in a second switching condition.
 2. An electric switching device as set forth in claim 1, and an electric heater located adjacent said bimetal element and terminal means for connecting said heater to a source of control current whereby the temperature of said bimetal element varies with the amplitude of the applied control current.
 3. An electric switching device according to claim 2 in which said bimetal element forms part of a bimetal system which includes a second bimetal element arranged to provide compensation for changes in ambient temperature.
 4. An electric switching device according to claim 3 in which said electric heater comprises a member separate from said bimetal element and adapted to be maintained in close proximity to and to follow the movement of ssid bimetal element.
 5. An electric switching device in accordance with claim 4 in which said bimetal element is of flat blade form and said electric heater is of similar strip-like shape.
 6. An electric switching device in accordance with claim 5 in which said electric heater is of ceramic substrate type.
 7. An electric switching device according to claim 5 in which said electric heater is supported by means of light flexible blade springs to abut said bimetal element without imparting any substantial displacement force thereto.
 8. An electric switching device in accordance with claim 3 in which said bimetal system comprises two blade-form bimetal elements in spaced parallel relationship and rigidly interconnected with one another at one end, the opposite end of one blade element being fixed in position and forming an ambient temperature compensating member and the opposite end of the other blade element being coupled to said latching lever system.
 9. An electric switching device according to claim 2 in which said latching lever system comprises two latch levers arranged to permit the respective closing and opening operations of said switch contacts to occur at different levels of energization of said electric heater.
 10. An electric switching device according to claim 9 in which the closing operation of said switch contacts is arranged to occur at a level of energization of said electric heater which is higher than the subsequently occurring level of heater energization at which opening of said switch contacts occurs.
 11. An electric switching device according to claim 9 in which said two latch levers are disposed in side-by-side relationship and independently pivoted upon a common pivot pin, one of said latch levers being coupled to said bimetal element in a manner providing positive transmission of movement from such bimetal element in each of two opposing directions and the other of said latch levers being spring biased into coupling engagement with said bimetal to provide positive transmission of movement in one direction only.
 12. An electric switching device in accordance with claim 2, and light sensing means connected to supply energizing current to said heater and at least one electric lamp connected for energization from a current supply source through said first and second contacts.
 13. An electric switching device comprising stationary frame means, first and second resilient spring blades each secured at one end to said frame means and disposed in parallel facing relationship and each carrying one of a pair of cooperating electric contacts, a strip-form first bimetal element, a second ambient-temperature compensating bimetal element secured at one end to said frame means and at its other end to one end of said first bimetal element, an electric heater having terminal means for connection to a source of switch control current, resilient support means operative to maintain said heater in close heat transfer relationship to said first bimetal element during displacement of such first bimetal element during heating and cooling thereof and first and second latch levers each pivotally mounted on a common pivot secured to said frame means, each of said latch levers being coupled to the other end of said first bimetal element for rocking movement in accordance with the heating and cooling of said first bimetal element, said first latch lever having a nose operative during displacement of said first bimetal element in one direction to urge said first spring blade towards said second spring blade and a latch-forming limb cooperating with said second spring blade to maintain said contacts separated from one another until a latch tripping point is reached during said movement in said one direction and said second latch lever having a latch-forming limb cooperating with said first spring blade to maintain said contacts engaged with one another until a latch tripping point is reached during displacement of said first bimetal element in a direction opposite to said one direction. 